Refractive Variation Research Articles

Transmission-type angle deviation microscopy

We present a new microscopy technique that we call transmission angle deviation microscopy (TADM). It is based on common-path heterodyne interferometry and geometrical optics. An ultrahigh sensitivity surface plasmon resonance (SPR) angular sensor is used to expand dynamic measurement ranges and to improve the axial resolution in three-dimensional optical microscopy. When transmitted light is incident upon a specimen, the beam converges or diverges because of refractive and/or surface height variations. Advantages include high axial resolution (approximately 32 nm), nondestructive and noncontact measurement, and larger measurement ranges (+/- 80 microm) for a numerical aperture of 0.21 in a transparent measurement medium. The technique can be used without conductivity and pretreatment.

Modified Astigmatism Correction Nomogram

<H4>What About LASEK?</H4> <p><B>Reply:</B><br>We thank Dr Massimo Camellin for his letter, which appeared in the May 2008 issue of the <cite>Journal of Refractive Surgery</cite>. We would like to clarify that <cite>1977-2007: Commemorating the ISRS/AAO and Global Refractive Surgery</cite> was written to document the history of the International Society of Refractive Surgery of the American Academy of Ophthalmology (ISRS/AAO) and the individuals who contributed significantly and/or were prominently involved in the formation and growth of the ISRS from its early formation with Drs Jose I. Barraquer, Richard C. Troutman, Miles H. Friedlander, and Casmir A. Swinger to the eventual merger with the AAO. The book was not intended to be a history of refractive surgery techniques and variations.</p>

Synthesis and optical properties for crystals of a novel organic semiconductor [ Ni(Cl) 2{(Ph 2P) 2CHC(R 1R 2)NHNH 2}

In this investigation, the synthesis process of the apyrazole derivative for diphenylphosphino-methane hydrazine complexes [ Ni(Cl)2{(Ph2P)2CHC(R1R2)NHNH2}] was reported, and the obtained crystals were analyzed by X-ray diffraction. As a result of the growth process, a set of complexes were formed. The structures of these complexes are discussed on the basis of Elemental analysis (EA), IR, 1H-NMR, 31P-NMR spectroscopic data and FAB mass spectra. The compound under investigation shows typical semiconductor behavior as a result of delocalization of the π-electrons in the structure. The reflectance and transmittance spectra for the crystals were measured and analyzed in the incident photon energy range 1.29 to 3.93 eV and in the temperature range 77 to 300 K. The optical study revealed that the optical transition is direct allowed. Below the absorption edge, the refractive index as a function of wavelength was determined in the low energy region of the used incident photon energy range. From the refractive index-wavelength variations, the oscillator and dispersion energies of the refractive index for the obtained crystals were determined. The static refractive index and static dielectric constant were evaluated.

Phase imaging with thermal neutrons

Across four decades, Sam Werner has built and performed elegant neutron interferometry experiments to measure a variety of quantum mechanical phases. These experiments have stringent requirements on experimental conditions and neutron beam conditioning. However, since refractive variations within a sample redistribute neutron intensity transverse to the propagation direction, a simple experimental geometry permits non-interferometric phase measurement and relaxes beam-conditioning requirements. This phase imaging technique, based on the transport of intensity equation, has advantages of allowing weakly absorbing samples to be radiographed at greatly reduced radiation doses, and enabling the use of polychromatic neutrons to increase flux and speed imaging. Furthermore, using other radiations, phase vortices like those of the Aharonov–Bohm effects have been observed.

Radio science measurements of atmospheric refractivity with Mars Global Surveyor

Radio occultation experiments with Mars Global Surveyor measure the refractive index of the Martian atmosphere from the surface to ~250 km in geopotential height. Refractivity is proportional to neutral density at low altitudes and electron density at high altitudes, with a transition at ~75 km. We use weighted least squares to decompose zonal refractivity variations into amplitudes and phases for observed wave numbers k = 1–4 over the entire altitude range and use the results to analyze atmospheric structure and dynamics. The data set consists of 147 refractivity profiles acquired in December 2000 at summer solstice in the Martian northern hemisphere. The measurements are at an essentially fixed local time (sunrise) and at latitudes from 67° to 70°N. Thermal tides appear to be responsible for much of the observed ionospheric structure from 80 to 220 km. Tides modulate the neutral density, which in turn, controls the height at which the ionosphere forms. The resulting longitude‐dependent vertical displacement of the ionosphere generates distinctive structure in the fitted amplitudes, particularly at k = 3, within ±50 km of the electron density peak height. Our k = 3 observations are consistent with an eastward propagating semidiurnal tide with zonal wave number 1. Relative to previous results, our analysis extends the characterization of tides to altitudes well above and below the electron density peak. In the neutral atmosphere, refractivity variations from the surface to 50 km appear to arise from stationary Rossby waves. Upon examining the full vertical range, stationary waves appear to dominate altitudes below ~75 km, and thermal tides dominate altitudes above this transition region.

Variations of the Tropospheric Refraction over the Sea. Simultaneous Measurements at Ground-to-Ground and Satellite-to-Ground Radio Paths

Variations of the Tropospheric Refraction over the Sea. Simultaneous Measurements at Ground-to-Ground and Satellite-to-Ground Radio Paths

Avaliação da eficácia da facectomia com implante de lente intra-ocular na infância

To evaluate the efficacy of the use of intraocular lenses in the treatment of pediatric aphakia, according to postoperative visual acuity and refraction change. A total of 33 eyes in 27 children were studied. Children with either unilateral or bilateral cataracts were submitted to lensectomy surgery via pars plana, with intraocular lens implant, associated with primary posterior capsulectomy and anterior vitrectomy. The intraocular lenses were calculated for emmetropia in the first postoperative month. All children were less than six years old at the time of the surgery and had a 2.9 year average follow-up. They were divided into 3 groups. Group I (10 eyes), children with unilateral cataracts and under three years old at the time of the surgery; group II (11 eyes), children with unilateral cataracts and above three years old; group III (12 eyes), children with bilateral cataracts and above three years old at the time of the surgery. On the last follow-up examination recorded visual acuity was equal to or above 20/40 in 85% of the eyes. A spherical equivalent close to emmetropia in the first postoperative month was obtained in 70% of the children of group III but only in 30% of group I. Regarding postoperative refraction variation, myopic shift was detected in 81.81% of the cases. The younger the children were when undergoing surgery, the greater the refractional alteration. Despite the myopic shift that happens with the use of intraocular lenses in the treatment of pediatric aphakia in children under six years old, the visual result is very good and the residual refraction correction is easily performed. A more prolonged postoperative follow-up would be necessary for long-term evaluation of the results.

Refractive indices variation with temperature and humidity of optical adhesive

Refractive index and birefringence of optical adhesives is studied under different environmental exposures, such as temperature, humidity, and annealing. Refractive index of the adhesive decreases at a higher rate for the temperature treatment compared to the humidity exposure. A sudden decrease in the rate of refractive index (thermo-optic coefficient, dn/dT), from −2×10−4°C−1 to −4×10−4°C−1 was observed near the glass transition temperature. The adhesive’s refractive index (n) was studied during the moisture desorption cycle. Refractive index of the adhesive was found to increase at a constant rate with moisture. The change in refractive index of the adhesive upon moisture absorption was found to be irreversible. Birefringence (TE — TM) decreases with higher annealing temperature treatment of the adhesive, because the rate of increase in refractive indices for TE and TM modes is not similar. The refractive index in TM mode increases at a higher rate compared to that in the TE mode. This suggests that the material has become more isotropic due to annealing. The environmental changes in optical properties of the adhesive are discussed in light of Lorenz-Lorentz equations.

Light and Relativity, a Previously Unknown Eighteenth‐Century Manuscript by Robert Blair (1748–1828)*

In 1786, Robert Blair, an unknown astronomer from Edinburgh, wrote a paper that would remain unpublished. In his manuscript, Blair gives a systematic treatment of the Newtonian kinematics of light, taking into account in the absolute space of Newton the motion of the light source, that of the observer, and the velocity of the corpuscles of light. Two years before, in the context of Newton's corpuscular theory of light, John Michell had pointed out that the velocity of light could be measured with the help of refraction experiments. Blair went a step further and inferred the existence of what we now call the Doppler effect: a variation of refraction due to a relative motion of the source and the observer. Blair's proposal is at the roots of Arago's well‐known 1806–10 experiments on the velocity of light. In the context of the undulatory theory of light, Blair proposed an experiment to determine the absolute motion of the Earth, laying the bases for the famous experiment performed by Albert Michelson 100 years later. In fact, this manuscript contains the very questions of light relativity, the roots of spectroscopy, and addresses the very problems that would be hotly debated in the nineteenth century, only to be solved by Einstein in 1905. *At the request of the author, publication has been delayed to coincide with the anniversary of Einstein's paper on special relativity.

Scintillation of short duration records

We have investigated propagation of sound in the ocean using the theory of wave propagation in random media. The theory classifies specific source/receiver geometries as either unsaturated, partially saturated, or saturated. In the unsaturated regime the variance of the intensity fluctuations will generally be quite small such that the scintillation index is less than unity. The partially saturated regime can give rise to scintillation indices larger than unity. In the fully saturated regime the scintillation index asymptotically approaches unity. We have conducted an experiment in which the two-dimensional sound-speed field was measured directly using a towed CTD chain, and relatively short acoustic records were captured using a number of source/receiver pairs. The length scales and index of refraction variation place the experiment in the saturated regime. However, measured scintillation indices are much less than 1. We provide an explanation for this difference and utilize local current measurements to bring the theory into agreement with the data. Our results are applicable to operational sonar systems, where short duration records are ordinarily utilized to transmit information or detect targets. [Work sponsored by ONR Code 321US.]

Optical characterisation of thin film cadmium oxide prepared by a modified reactive thermal evaporation process

The optical transmission spectra of transparent conducting cadmium oxide (CdO) thin films deposited by a modified reactive evaporation process onto glass substrates have been measured. The interference fringes were used to calculate the refractive index, thickness variation, average thickness and absorption coefficient of the films. The influence of the partial pressure of oxygen (PO2), during film deposition on the transmittance, optical constants and bandgap of the films is studied. The observation of an optimum value of PO2­ (= 0.040 Pa) at which the transmission is maximum is considered to be a particularly significant result. So, too, is the result that the width of the bandtail has a minimum at the optimum PO2 value. Key words: CdO Films, Optical Transmittance, Evaporation (Global Journal of Pure and Applied Sciences: 2003 9(4): 567-574)

Approximate analytic solutions for diffraction by non-uniform reflection geometry fiber Bragg gratings

Approximate analytic expressions for the transmitted and diffracted fields from a non-uniform in-fiber Bragg grating are presented, in terms of Hermite and Kummer confluent hypergeometric functions. These novel approximate analytic solutions are derived for the case of a grating having both a weak linear variation of grating period with length (weak linear chirp) and a quadratic approximation to a Gaussian refractive index modulation variation. The solution is derived using the Beta-value first-order two-wave coupled differential equations and describes both on- and off-Bragg replay. The equations are shown to be useful, when compared to more exact numerical results, for a wide range of practical grating parameter values.

Tropospheric Gradient Estimation at CODE: Results from Global Solutions

Observations at low elevation angles are gathered and used for high accuracy GPS analyses. Introducing tropospheric gradient parameters in the estimation process allows it to take into account of azimuthal variations of tropospheric refraction. This measure significantly improves the repeatability of station coordinates. Most of the mean gradients for stations in the northern and the southern hemisphere show a similar behavior. By combining several years of data from a global solution results a consistent pattern.

Electromagnetic-field distribution measurements in the soft x-ray range: full characterization of a soft x-ray laser beam.

We report direct measurement of the electromagnetic-field spatial distribution in a neonlike Ar capillary discharge-driven soft x-ray laser beam. The wave front was fully characterized in a single shot using a Shack-Hartmann diffractive optics sensor. The wave front was observed to be dependent on the discharge pressure and capillary length, as a result of beam refraction variations in the capillary plasma. The results predict approximately 70% of the laser beam energy can be focused into an area 4 times the size of the diffraction-limited spot, reaching intensities of approximately 4 x 10(13) W/cm(2).

Polarized angular dependent spectroscopy of epithelial cells and epithelial cell nuclei to determine the size scale of scattering structures.

An understanding of the relationship between tissue structures and light scattering from tissue will help facilitate the development and acceptance of noninvasive optical diagnostics including elastic scattering spectroscopy, diffuse reflectance, and optical coherence tomography. For example, a quantitative model of the structures that scatter light in epithelial cells would allow determination of what structures control the characteristics of in vivo light transport measurements and subsequently could provide a detailed relationship between cellular structures and optical measurements. We have determined the size distribution of refractive index structure variations in epithelial cells as well as in nuclei isolated from epithelial cells from measurements of the angular dependence of polarized light scattering. The quantitative size distributions we obtained for both whole cells and isolated nuclei include particles with effective radii of 2 microm to 10 nm or less and contain orders of magnitude more small particles than large particles. These results demonstrate that not only are biological cells very heterogeneous, but so are the nuclei within them. Light scattering is likely sensitive to structures smaller than those commonly investigated by standard pathology methods.

Tropospheric delay estimation and analysis using GPS and SAR interferometry

Spatially localized refractivity variations, mainly due to water vapor, are a major source of error in high-precision positioning techniques such as GPS and SAR interferometry. Refractivity induced delay variations can be misinterpreted as, e.g., crustal deformation signals or positioning biases. In this study, signal delay estimates based on SAR observations and simultaneous GPS time series are quantitatively compared. Wind speed and wind direction estimates are used to relate the temporal zenith delays derived from GPS with the spatial slant delays observed by SAR interferometry, assuming a static refractivity distribution transported by the wind. Five case studies show significant correlation between both techniques, mainly limited by the GPS epoch length, zenith averaging, and the degree of similarity in wind direction during the two SAR acquisitions. RMS differences varied between 2 and 10 mm, while the total delay variability spanned 15–60 mm. The results show that it can be possible, under suitable atmospheric circumstances, to approximate the amount of delay variation with wavelengths >5 km in a strip of a SAR interferogram using GPS, wind speed, and wind direction measurements.

Monocular diplopia related to asymmetric corneal topography after laser in situ keratomileusis.

To show a specific relationship between monocular diplopia and corneal refractive asymmetry after laser in situ keratomileusis (LASIK). One hundred thirty-eight eyes of 98 patients who underwent LASIK for myopia between -2.12 and -17.75 D were examined under room-lighted conditions. We examined 51 eyes at 2 weeks, 46 eyes at 3 months, 32 eyes at 6 months, and 9 eyes at 1 year after LASIK. We attempted to correlate the presence of monocular diplopia with their corneal topographical features. Eight eyes of five patients (five eyes at 2 weeks, three eyes at 3 months after LASIK) produced symptoms of monocular diplopia. These symptomatic patients had a common corneal topographical feature caused by decentralized or inhomogeneous ablation. Every pupillary area in the patients' topographies contained steeper and flatter areas. The range of refractive power variation in these asymmetric areas was at least 1.50 D. The location of the secondary image correlated with the direction of the steeper area in all eight eyes. Pinhole viewing eliminated or reduced the prominence of secondary images in every case. Monocular diplopia following LASIK appears to correlate with postoperative corneal refractive power variation inside the pupillary area, caused by decentralized or inhomogeneous ablation.

Comparison of Precipitable Water Vapor Observations by Spaceborne Radar Interferometry and Meteosat 6.7-μm Radiometry

Abstract Satellite radar interferometry (InSAR) can be applied to study vertically integrated atmospheric refractivity variations with a spatial resolution of 20 m and an accuracy of 2 mm, irrespective of cloud cover or solar illumination. The data are derived from the difference between the radar signal delay variations within the imaged area during two acquisitions with a temporal separation of one or more days. Hence, they reflect the superposition of the refractivity distribution during these two acquisitions. On short spatial scales, integrated refractivity variations are dominantly caused by spatial heterogeneities in the water vapor distribution. Validation of the radar interferometric results can be difficult, since conventional imaging radiometers do not provide quantitative measures for water vapor content over the entire tropospheric column and are lacking in spatial resolution. Moreover, comparable quantitative data such as signal delay observed by Global Positioning System (GPS) receivers are...

Development of stereoscopic molecular tagging velocimetry

This paper describes the development of a stereoscopic molecular tagging velocimetry (sMTV) technique for measuring the instantaneous three-component velocity field over a plane in a flow. The calibration technique employed allows the stereo imaging parameters to be determined directly from a target image without the direct physical measurement of those parameters. Effects of index of refraction variations are accounted for approximately in the calibration method. Sensitivity analysis and target test experiments for a typical optical setup indicate maximum error levels for the in-plane components to be nominally the same as two-component MTV measurements. The error in the out-of-plane velocity component can be one to three times larger, depending on the stereo viewing angle. Experimental results are presented to validate the sMTV technique against other known measured results, along with an application to the highly three-dimensional flow field near the tip of a model propeller.

Refraction and Anterior Chamber Depth Change After Vitrectomy for Pseudophakia

Purpose: To evaluate the association between the vitreous and the refractive error in pseudophakia. Methods: Vitrectomy was performed in 67 eyes of 61 patients who underwent cataract surgery. Vitrectomy was needed for epiretinal membrane in 30 eyes, macular edema in 22 eyes, macular hole in 3 eyes, lamelar macular hole in 2 eyes, macular hole in 3 eyes, lamelar macular hole in 2 eyes, vitreous opacity in 6 eyes, and vitreous hemorrhage in 4 eyes. Refraction was measured before the operation, and 1 month, 3 months, 6 months, and 12 months after operation. Anterior chamber depth was measured in 10 eyes before the operation, and 1 month, 3 months, and 6 months after operation. We evaluated the refractive error after vitrectomy in 49 eyes that had predicted refraction. Results: The mean value of refractive change was −0.3 D 1 month postoperatively, and then gradually became positive. The variation of refraction (6-month postoperative refraction minus preoperative refraction) was negatively correlated with preoperative refraction ( P = .0052, R 2 = 0.146). If preoperative refraction was more myopic than −1.5 D, then refraction became positive. If preoperative refraction was not more myopic than −1.5 D, then refraction became negative. Conclusion: About 15% of postoperative refractive error may be associated with the vitreous, but further investigation is required.